<%@ page import="java.util.ArrayList" %>
<%@ page import="java.util.HashMap" %><%--
  Created by IntelliJ IDEA.
  User: 14533
  Date: 2022/1/30
  Time: 14:52
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    <%
        // 1、值为 null 值的时候，为空
        request.setAttribute("emptyNull", null);
        // 2、值为空串的时候，为空
        request.setAttribute("emptyStr", "");
        // 3、值是 Object 类型数组，长度为零的时候
        request.setAttribute("emptyArr", new Object[]{});
        // 4、list 集合，元素个数为零
        request.setAttribute("emptyList", new ArrayList<>());
        // 、map 集合，元素个数为零
        request.setAttribute("emptyMap", new HashMap<>());
    %>

    ${empty emptyNull} <br/>
    ${empty emptyStr} <br/>
    ${empty emptyArr} <br/>
    ${empty emptyList} <br/>
    ${empty emptyMap} <br/>

    <hr/>
    ${12 == 12? "是的": "不是"}
</body>
</html>
